Interlocked molecules templated catenane synthesis

Fortunately, more efficient methods for the complexation of macrocyclic hosts with acyclic guest molecules have become available with the advent of supramo-lecular chemistry, resulting in higher yields in rotaxane and catenane synthesis. In the following sections, the preparation of different types of interlocked molecules, with the use of host-guest recognition, is discussed. It should be noted that these template-directed methods differ significantly from the above-mentioned stochastic approach [28]. 

The synthesis of interlocked molecules has become commonplace over the past 25 years with the gradual development of a number of highly facile template methods for their construction. What were once laboratory curiosities have now taken a prominent place in the broad field of supramolecular chemistry, especially regarding their uses and further potential as molecular switches and machines [1], We present here an overview of the main synthetic approaches to these molecules, with a focus on methods in which macrocyclization reactions result in interlocked products. The analysis is by no means meant to be comprehensive or exhaustive in detail, but rather to convey the variety and utility of the selected synthetic strategies in generating abiotic rotaxane and catenane superstructures. 

The interest in rotaxanes, pseudorotaxanes, and catenanes (i.e., molecules that contain non-covalently interlocked components) stems from their potential use as building blocks in molecular devices. Their syntheses usually rely on some sort of template assistance, such as the preorganization of the assembly s components around a metal center. While cationic templates have been widely used in this context, only a few examples of anion-directed synthesis of interlocked molecules have been reported. In fact, although rotaxanes and pseudorotaxanes have been prepared in this way (as discussed in this section), to date there is no reported example of anion-directed synthesis of catenanes. 

During the past 20 years, mechanically interlocked molecules, known as catenanes and rotaxanes, many of them redox-active, have become readily accessible using template-directed protocols that rely upon the precepts of molecular recognition and self-assembly and the tenets of supramolecular assistance to covalent synthesis. By incorporating different recognition units with dissimilar redox properties into appropriate components, these compounds can often be induced to switch hysteretically between ground and metastable co-con-... 

Owing to the development of supramolecular chemistry and a series of efficient synthetic methods such as template synthesis and dynamic covalent synthesis, artificial molecular machines have exploded since the late 1980s. In this chapter, we mainly discuss mechanical molecular machines that is, the different components among the molecules or supramolecular aggregates, which are linked by noncova-lent interactions and are usually called mechanical bonds. Mechanical bonds, in which two or more molecular components become mechanically interlocked, one with another," play a dominant role in the development of artificial molecular machines. Threaded structures, such as pseudorotax-anes, rotaxanes, and catenanes, are excellent precursors in the construction of molecular machines, for the mechanical bonds in these supramolecular systems are easy to be altered by external stimuli, causing relative movements among different components. Molecular rotors and propellers are also discussed because of their great importance in the development of motorized machines. 

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